Here are a heap of cheats for Midnight Club 3: DUB Edition Remix. For all of the following enter the cheat codes at the cheat menu to unlock the cheat that you want.
In all cases, they cheat menu is here :: Main Menu >> Options >> Cheats
Unlock all cities in arcade mode Roadtrip
Increase car mass in arcade mode Hyperagro
Unlock Argo special move Dfens
Unlock Roar special move Rjnr
Unlock Zone special move Allin
No damage Ontheroad
Faster pedestrians Urbansprawl
And here are some of the funny ones...
Get a bunny head Getheadl
Get a flaming head Trythisathome
Get a pumpkin head Getheadk
Get a skull head Getheadn
Get a snowman head Getheadm
Get a yellow smile head Getheadj
Get a chrome body Haveyouseenthisboy
Get more money Enter "kubmir" at the cheat menu. Adds one dollar so you'll need some kind of auto fire to amass some bucks quickly... Try this... After you have entered the code, press R2 and set the word "kubmir" to the top slot. Now set R2 and X to auto-fire. Hold down the R2 and X and hopefully the bucks will start to roll in.